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Digestive System-I PowerPoint Presentation

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Description : The digestive system consists of the digestive tract: oral cavity, mouth, esophagus (ANTERIOR PART), stomach, small and large intestines, (MIDDLE PART), rectum, and anus (POSTERIOR PART) – and its associated glands – salivary glands, liver, and pancreas.

Tags : digestive system, digestive tract, mucosa, submucosa, muscularis externa serosa, adventitia

Published on : Oct 25, 2020 | Views : 2228 | Downloads : 1

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Digestive System-I
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The digestive system consists of the digestive tract: oral cavity, mouth, esophagus (ANTERIOR PART) stomach, small and large intestines, (MIDDLE PART) rectum, and anus (POSTERIOR PART) – and its associated glands – salivary glands, liver, and pancreas.
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GENERAL STRUCTURE OF THE DIGESTIVE TRACT The alimentary canal is composed of following concentric layers: mucosa, submucosa, muscularis externa serosa or adventitia.
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The mucosa (I), the innermost layer, comprises: 1) epithelial lining: 2/ lamina propria of loose connective tissue 3/ muscularis mucosae of SMC
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lamina propria Lamina propria of loose connective tissue rich in blood and lymph vessels, sometimes also containing glands (simple glands) and lymphoid tissue (diffuse cells or solitary lymphoid follicles) The pyloric part of the stomach
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Muscularis mucosae, usually consists of a thin inner circular layer and outer longitudinal layer of smooth muscle cells, separating the mucosa from the submucosa.
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The submucosa is composed of loose connective tissue rich in elastic fibers component with many large blood and lymph vessels and a submucosal (also called Meissner’s) nerve plexus. It may also contain glands (compound glands) and lymphoid tissue.
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The submucosa
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The muscularis externa The muscularis externa contains usually smooth muscle cells
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The outermost layer of the alimentary canal is either a serosa or an adventitia. The intraperitoneal regions of the alimentary canal possess a serosa. It is a thin layer of loose connective tissue, rich in blood and lymph vessels and adipose tissue, and covered by a mesothelium (a simple squamous covering epithelium)
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Intestinal-associated lymphoid tissue is the largest part of the immune system containing up to 40% of all immune effector cells of the body. The lymphoid tissue constitutes 25% of the intestinal mass.
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ТHE ORAL CAVITY Oral region includes the lips, teeth (and associated structures), palate, tongue, tonsils, as well as the major salivary glands. I. The oral cavity is lined with nonkeratinized stratified squamous epithelium. Regions of partially keratinized epithelium are: filiform papillae of the dorsal surface of the tongue; the gum epithelium; the marginal zone of the hard palate epithelium; “pale line” of the intermediate zone of the cheek mucosa
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The tongue’ dorsal surface is irregular, covered anteriorly by a great number of small eminences called papillae.
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Filiform papillae have an elongated conical shape; they are quite numerous and are present over the entire surface of the tongue. Their epithelium, which does not contain taste buds, is frequently partly keratinized.
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Fungiform papillae contain scattered taste buds on their upper surfaces.
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Foliate papillae are poorly developed in human adults. They consist of 2 or more parallel ridges and furrows on the dorsolateral surface of the tongue.
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Circumvallate papillae are surrounded by an epithelially lined groove and have taste buds.
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Each tooth has the following named parts: CROWN (corona) – projects above the gingiva (gum) and is the only part covered by enamel ROOT (radix) projects below the gum into the bony socket (alveolus); covered by cementum. A small opening at the root’s apex (apical foramen) provides vessels and nerves access to the pulp cavity NECK (cervix) is the point where enamel and cementum meet (crown-root junction)
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PULP CAVITY lies at the core of tooth; it is filled with pulp, a loose connective tissue Upper part is pulp chamber. Lower part is root canal.
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Hard (calcified) components of the tooth: enamel, dentin, cementum, alveolar bone.
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Soft components of the tooth and associated structures: pulp; mucosa of adjacent gum; periosteum of alveolar bone; periodontal ligament
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Dentin comprises the main portion of the tooth Dentin envelops the pulp cavity in both the crown and root. Dentin is covered by enamel at the crown; is covered by cementum at the root. Dentin is subtype of bone tissue COMPOSITION: Dry weight - 72% inorganic components (hydroxyapatite crystals mainly; calcium fluoride, calcium, magnesium, sodium carbonates); 28% organic components; water - 8-12%. The principal organic component is type I collagen glycosaminoglycans
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Dentin is softer than enamel but harder than bone Produced by odontoblasts Unlike bone, dentin does not contain cell bodies and blood vessels. Bodies of odontoblasts, (the cells secreting dentin) lye outside the dentin, within the peripheral layer of the pulp; Long, branched odontoblast process (Tomes’s fiber) extends from each cell’ apical (dentinal) surface and penetrates the dentin’s width in a dentinal tubule (30 000 – 75 000 dentinal tubules/ 1 sq.mm)
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Enamel covers the tooth crown; Composition: mineral salts (mainly hydroxyapatite) make up 95% of enamel, making it the body’s hardest substance; organic components make up 1-5%; do not include collagen; organic components are presented by: non-collagenous proteins – amelogenins, enamelin
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CEMENTUM is calcified tissue, covering the dentin of the root and the neck in a very thin layer. It contains attachment fibers that help to anchor the tooth within the bone. СOMPOSITION: 50-60% inorganic substances (hydroxyapatite crystals mainly) 40-50% organic substances (collagen fibers and ground substance) and water. It is not as hard as enamel or dentin, but it is harder than bone. Cementum resembles reticulofibrous (woven) bone tissue, but lacks blood vessels, nerves
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ESOPHAGUS This part of the gastrointestinal tract is a muscular tube whose function is to transport foodstuffs from the mouth to the stomach. In general, it has the same layers as the rest of the digestive tract.
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ESOPHAGUS In the submucosa are groups of small mucus-secreting glands, the esophageal glands proper. They are compound tubuloalveolar glands. Muscularis externa is unusual in that it is composed of skeletal striated muscle in the upper one-third; a mixture of skeletal and smooth muscles in the middle one-third; and smooth muscle in the lower one-third. Only that portion of the esophagus in the peritoneal cavity (below the diaphragm) is covered by serosa. The rest is covered by a layer of loose connective tissue, the adventitia, which blends into the surrounding tissue.
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SALIVARY GLANDS There are 3 pairs of large salivary glands in addition to the small glands scattered throughout the oral cavity: the parotid, submandibular and sublingual glands. Each salivary gland is a compound acinar (alveolar) or tubuloacinar gland. All glands possess merocrine mode of the secretion. These glands consist of 2 general types of secretory cells – serous and mucous.
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Serous cells are usually pyramidal in shape with a broad base resting on the basal lamina and a narrow apical surface with short, irregular microvilli facing the lumen. They exhibit characteristics of polarized protein-secreting cells. Their cytoplasm contains extensive rough endoplasmic reticulum, a well-developed Golgi complex, and numerous mitochondria. The apical part usually contains secretory granules. Serous cells form serous secretory portions, a spherical mass of cells called an acinus (alveolus) with a lumen in the center.
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Mucous cells are usually cuboidal to columnar in shape; their nuclei are dark, flattened and pressed toward the bases of the cells. They present the characteristics of mucus-secreting cells. Mucous cells are most often organized as tubular mucous secretory portions. Mucous units consist of cylindrical array of secretory cells surrounding a lumen.
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In mixed secretory portions, serous and mucous cells are arranged in a characteristic pattern. The mucous cells form tubules, but their ends are capped by serous cells, which constitute the serous demilunes. Serous demilune cells deliver their secretions into intercellular spaces between the neighboring mucus-producing cells.